Radar (RAdio Detection And Ranging) is an object-detection system that uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect various object, such as: aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain.
The simplest function of radar is to tell how far away an object is. To do this, the radar device emits a concentrated radio wave and listens for any echo. If there is an object in the path of the radio wave, it will reflect some of the electromagnetic energy, and the radio wave will bounce back to the radar device. Radio waves move through the air at a constant speed (the speed of light), so the radar device can calculate how far away the object is based on how long it takes the radio signal to return.
Radar can also be used to measure the speed of an object, due to a phenomenon called Doppler shift. Like sound waves, radio waves have a certain frequency, the number of oscillations per unit of time. When the radar system and an object are both standing still relative to each other, the echo will have the same wave frequency as the original signal. But when the object is moving relative to the radar system, each part of the radio signal is reflected at a different point in space, which changes the wave pattern. When the object is moving away from the radar system, the second segment of the signal has to travel a greater distance to reach the car than the first segment of the signal. This has the effect of “stretching out” the wave, or lowering its frequency. If the object is moving toward the radar system, the second segment of the wave travels a shorter distance than the first segment before being reflected. As a result, the peaks and valleys of the wave get squeezed together and the frequency increases. The radar system can determine the relative speed of the object based on the Doppler frequency changes.
Clutter refers to radio frequency (RF) echoes returned from targets which are uninteresting to the radar application. Such targets include natural objects such as ground, pavement, puddles, precipitation (such as rain, snow, or hail), blowing sand or dust, atmospheric turbulence, other atmospheric effects, etc., for example.
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.